Signal modulators are utilized in a number of applications, for instance as part of the conversion from analogue signals to digital signals or vice versa.
Conventionally analogue-to-digital converters (ADCs) and digital-to-analogue converters (DACs) are implemented using multiple analogue components such as banks of well-matched or ratioed resistors, capacitors or current sources. However there is an ongoing trend to smaller semiconductor process node geometries and such circuitry does not scale efficiently in terms of semiconductor area and/or power requirements.
Time encoding modulators are modulators that encode input data into a time-encoded data stream. For example sigma-delta (ΣΔ) modulators (SDM's) are a type of time encoding modulator. SDMs may be used to convert an input analogue signal into a pulse-density-modulated (PDM) signal comprising a series of digital ones and zeros at a fixed sample rate and the relative density of ones and zeros corresponds to the analogue signal's amplitude. However the fixed frequency inevitably introduces quantisation noise into the signal, and SDMs usually comprise also at least one full operational amplifier. Time encoding modulators may also encode an input signal into a pulse-width modulated signal, by comparing the input signal with a periodic reference signal, such as a triangular waveform to encode the input signal by the duration of pulses in the output signal. However this requires circuitry to generate an appropriately accurate periodic reference signal and/or operational amplifier circuitry.
In general therefore there is thus a desire for smaller and/or lower power modulators that can be used, for example, as part of a signal converter such as an ADC or DAC.